1. Field of the Invention
The present invention relates generally to a disc base board molding die including a stamper plate attaching/detaching device. More particularly, the present invention relates to an improvement of an injection molding die of the foregoing type which ensures that the working stroke of a stamper plate attaching/detaching bush can be enlarged in the axial direction at the time of attachment/detachment of the stamper plate attaching/detaching bush, and moreover, a volume occupied by an actuating mechanism installed in the disc base board molding die can be minimized.
2. Description of the Prior Art
To facilitate understanding of the present invention, a typical conventional stamper plate attaching/detaching device installed in a disc base .board molding die will briefly be described below with reference to FIG. 3 and FIG. 4, each of which shows by way of example problems inherent to the conventional stamper plate attaching/detaching device.
FIG. 3 is a conventional stamper plate attaching/detaching device installed in a disc base board molding die, particularly showing a mode of operation of the stamper plate attaching/detaching device. Specifically, FIG. 3(L)shows by way of sectional view the operative state of the stamper plate attaching/detaching device wherein a stamper plate is firmly placed on the die cavity of a lower die half of the disc base board molding die, and FIG. 3(R) shows by way of sectional view the operative state of the stamper plate attaching/detaching device directly before the stamper plate is detached from the lower die half. The structure of the stamper plate attaching/detaching device is disclosed in an official gazette of Japanese Patent Laid-Open Publication NO. 2-60502.
As is best seen in FIG. 3(R), the stamper plate 2 is firmly attached around the outer periphery of a flange portion of a stamper plate attaching/detaching bush (hereinafter referred to simply as a bush) 3 in such a manlier that the stamper plate is snapped below the flange portion of the bush 3. Subsequently, the bush 3 is received in a tapered bush fitting hole 4.
A key slot 5 is formed in a cylindrical portion of the lower die half 1 located below the bush/fitting hole 4 for the purpose of preventing the bush 3 from being rotated during each stamper plate attaching/detaching operation, i.e., for the purpose of allowing the bush 3 to be linearly displaced in the upward/downward direction. A plurality of female threads 10 are formed around the outer periphery of a cylindrical hole formed in a die plate 7 below the key slot 5 so as to come in threadable engagement with the male threads 6 on the bush 3.
The die plate 7 is integrated with the lower die half 1, and a key 8 is projected to enter the key slot 5 for the foregoing purpose. In addition, a face gear 9, disposed below a cylindrical portion of the die plate 7, has a plurality of gear teeth formed along the lower surface thereof. A plurality of female threads 10 are formed around the inner periphery of the face gear 9 to come in threadable engagement with a plurality of male threads 6 formed around the outer peripheral surface of the bush 3 at the lower part of the latter.
To actuate an assembly of the bush 3 and the face gear 9, an actuating rod 11 is horizontally arranged in the die plate 7, and a pinion gear 12 is formed at the fore end part of the actuating rod 11 to come in meshing engagement with the face gear 9.
Attachment of the stamper plate 2 to the lower die half 1 is achieved in the following manner.
The stamper plate 2 is first fitted around the flange portion of the bush 3. The bush 3 is then received in the tapered bush fitting hole 4, and thereafter, the key 8 is projected in the key slot 8 so as to prevent the bush 3 from being rotated. Subsequently, an operator rotates the actuating rod 11 with his hand to rotate the face gear 9 via the pinion gear 12, causing the bush 3 to be forcibly displaced in the downward direction via threadable engagement of the male threads 6 of the bush 3 with the female threads 10 of the face gear 9 without any rotation of the bush 3. On completion of the downward displacement of the bush 3, as shown in FIG. 3(L), the stamper plate 2 comes in close contact with the upper surface of the lower die half 1.
Next, detachment of the stamper plate 2 from the lower die half 1 will be described below.
The operator rotates the actuating rod 11 with his land in the reverse direction so as to rotate the face gear 9 in the reverse direction via the pinion gear 12, causing the bush 3 to be forcibly displaced in the upward direction, whereby the stamper plate 2 is detached away from the lower die half 1.
An advantageous effect of the stamper plate attaching/detaching device constructed in the above-described manner consists in that the bush 3 is designed to have a large working stroke H.sub.1 as seen in the vertical direction, resulting in the bush 3 being safely detached from the lower die half 1 together with the stamper plate 2.
However, the stamper plate attaching/detaching device has a drawback in that the assembly of the face gear 9 and the pinion gear 12 occupies a large space in the die assembly on the movable side (consisting of the lower die half 1 and the die plate 7 in the illustrated case), causing die cooling circuits (not shown) to be restrictively formed in the die assembly on the movable side. Consequently, the whole structure of the disc base board molding die unavoidably becomes large in size. Another drawback is such that the actuating rod 11 is rotated by a large number of revolutions, causing each stamper plate attaching/detaching operation to be achieved in a long period of time.
For example, in the case where a gear ratio of the pinion gear 12 to the face gear 9 is set to 1:7, a pitch of each of the male threads 6 and the female threads 10 is set to 0.75 mm and the working stroke H.sub.1 of the bush 3 is set to 15 mm, it is necessary that the actuating rod 11 be rotated by 140 revolutions for achieving each stamper plate attaching/detaching operation. This means that it is practically difficult to manually rotate the actuating rod 11 with an operator's hand during the complete stamper plate attaching/detaching operation.
FIG. 4 is a sectional view of another conventional stamper plate attaching/detaching device installed in a disc base board molding die of which a patent application was filed by a common applicant to the present invention and has been laid open under Japanese Patent Laid-Open Publication NO. 2-295726.
The stamper plate attaching/detaching device includes a stamper plate attaching/detaching bush (hereinafter referred to simply as a bush) 13 of which the lower end part is designed in the form of a flange portion, and a stepped part 14 is formed around the flange portion of the bush 13. A lower die half 1 of the disc base board molding die is integrated with a die plate 15 through which two actuating rods 16 are inserted, and a part of the foremost end of each actuating rod 16 is cut out to form a flat plane portion 17 having a semicircular sectional shape.
Attachment of a stamper plate 2 to the lower die half 1 will be described below with reference to FIG. 4.
First, the stamper plate 2 is fitted around the outer periphery of the bush 13 and under a flange portion of the same, and the bush 13 is then provisionally inserted into a tapered fitting hole 4.
Prior to the provisionally insertion of the bush 13, the flat plane portion 17 of each actuating rod 16 is caused to extend past the axis line of the actuating rod 16 in the horizontal direction (see FIG. 4(L)), and thereafter, the left-hand actuating rod 16 is turned in the clockwise direction and the right-hand actuating rod 16 is turned in the anticlockwise direction so that the flat plane portions 17 are engaged with the stepped part of the bush 13, causing the bush 13 to be forcibly displaced ill the downward direction until the stamper plate 2 is brought in close contact with the upper surface of the lower die half 1.
Detachment of the stamper plate 2 from the lower die half 1 is achieved in such a manner that the left-hand actuating rod 16 is turned in the anticlockwise direction and the right-hand actuating rod 16 is turned in the clockwise direction, causing the bush 3 to be displaced by outer edge portions 18 of both actuating rods 16 in the upward direction (see FIG. 4(R)).
All advantageous effect of the stamper plate attaching/detaching device constructed in the above-described manner consists in that each attaching/detaching operation can be achieved merely by a turning movement of both actuating rods 17 by an angle of about 180 degrees so that the actuating mechanism is designed with a simple structure while occupying a minimized space in the die assembly on the movable side, resulting in the disc base board molding die being designed with an increased degree of design freedom and with small dimensions.
However, the stamper plate attaching/detaching device has a drawback that a working stroke H.sub.2 of the bush 13 is limited merely to about 2/3 of the outer diameter of each actuating rod 16, causing the detachment of the stamper plate 2 from the lower die half 1 to be achieved with some difficulty. For example, in the case where each actuating rod 16 has an outer diameter of 10 mm, the working stroke H.sub.2 of the bush 13 is set to a small value of only about 7 mm.
To ensure that the bush 13 is safely detached from the lower die half 1 together with the stamper plate 2, it is hitherto required that the working stroke of the bush 13 be set to about 15 mm or more.